[ADI][68/N] update installer targetSdkVersion check

CompatChange.EnabledAfter doesn't work when the current platform version
is older than the app's targetSdkVersion. Therefore, switch to directly
checking the installer app's targetSdkVersion instead of relying on
EnabledAfter.

FLAG: android.content.pm.verification_service
BUG: 360129657
Test: atest CtsRootDeveloperVerificationPrivInstallerTarget37TestCases
Test: atest CtsRootDeveloperVerificationInstallerTarget37TestCases
Test: atest CtsRootDeveloperVerificationPrivInstallerTarget36TestCases
Test: atest CtsRootDeveloperVerificationInstallerTarget36TestCases

Change-Id: Ifab9cee23e362b881446d5f1b0d967bcd5e78d37